The present invention relates to an improvement in a caliper of an opposed-piston disc brake that is used to brake a vehicle (for example, an automobile).
A disc brake is widely used to brake an automobile. When the disc brake is applied, a pair of pads, each of which is disposed on each of both axial sides of a rotor rotating along with a wheel, is pressed against both side surfaces of the rotor by pistons. In the related art, various structures of the disc brakes are disclosed, and in recent years, an opposed-piston disc brake, in which the pistons are provided on both sides of the rotor to face each other, has increasingly been used.
FIGS. 15 to 17 illustrate an example of the structure of the opposed-piston disc brake caliper in the related art disclosed in Patent Document 1. A caliper 1 is an integral cast component made of a light alloy such as an aluminum alloy or an iron alloy. The caliper 1 includes an inner body portion 2; an outer body portion 3; an entry-side connection portion 4; and an exit-side connection portion 5.
The inner body portion 2 among these portions is provided to face an inner-side surface (a side surface that faces the center of a center body in a lateral direction of the vehicle body when the disc brake is assembled in a vehicle) of a rotor 6 rotating along with a wheel. In contrast, the outer body portion 3 is provided to face an outer-side surface (a side surface that faces the outside in the lateral direction of the vehicle body when the disc brake is assembled in the vehicle) of the rotor 6. The entry-side connection portion 4 and the exit-side connection portion 5 are provided on the outside of an outer circumferential edge of the rotor 6 in a radial direction. The entry-side connection portion 4 between these portions connects an entry-side end portion of the inner body portion 2 to an entry-side end portion of the outer body portion 3. The exit-side connection portion 5 connects an exit-side end portion of the inner body portion 2 to an exit-side end portion of the outer body portion 3. An opening portion 7 is provided to radially pass through a region, the circumference of which is surrounded by both the inner body portion 2 and the outer body portion 3 and both the entry-side connection portion 4 and the exit-side connection portion 5. A circumferential intermediate portion of the inner body portion 2 is connected to a circumferential intermediate portion of the outer body portion 3 via a central bridge portion 8 that is provided on the outside of the outer circumferential edge of the rotor 6 in the radial direction while being disposed in a circumferential central portion of the opening portion 7. The central bridge portion 8 divides the opening portion 7 into two sections in the circumferential direction.
In the specification and the claims, unless specified, an axial direction, a circumferential direction, and a radial direction refer to the axial direction, the circumferential direction, and the radial direction of the rotor, respectively. Unless specified, an entry side refers to a region between both the inner body portion and the outer body portion which the rotor rotating along with the wheel during straight ahead traveling enters. An exit side refers to a region between both the inner body portion and the outer body portion from which the rotor moves away.
Inner cylinders 9, 9 and outer cylinders are respectively provided in surfaces of both the inner body portion 2 and the outer body portion 3 with the surfaces facing each other. FIG. 15 illustrates only the inner cylinders 9, 9. The outer cylinders having the same shape as that of the inner cylinders 9, 9 are also provided in the outer body portion 3 while the outer cylinders and the inner cylinders 9, 9 are disposed symmetrical to the rotor 6. In an assembled state of a disc brake apparatus, the inner cylinders 9, 9 open toward the inner-side surface of the rotor 6, and the outer cylinders open toward the outer-side surface of the rotor 6.
On the inside of the caliper 1, an inner pad 10 and an outer pad are supported in such a way as to be capable of being displaced in the axial direction while in use. For this reason, as illustrated in FIG. 17, a pair of projecting wall portions 11, 11 projecting in the axial direction are respectively provided in both circumferential end portions of each of side surfaces (an outer-side surface of the inner body portion 2 and an inner-side surface of the outer body portion 3) of the inner body portion 2 and the outer body portion 3 with the side surfaces facing each other. Metal support fittings 12, 12 are respectively fixed to radial inner surfaces of the projecting wall portions 11, 11 using bolts 13, 13. Both circumferential end portions of each of the inner pad 10 and the outer pad are engaged with engagement protruding parts 14, 14 of the metal support fittings 12, 12 in such a way that the inner pad 10 and the outer pad can be displaced in the axial direction, with the engagement protruding parts 14, 14 protruding from the radial inner surfaces of the projecting wall portions 11, 11 in the circumferential direction.
When the brake is applied, inner pistons press the inner pad 10, which is supported by the inner body portion 2, against the inner-side surface of the rotor 6, with the inner pistons being respectively fitted into the inner cylinders 9, 9 in an oil tight manner. Similarly, outer pistons press the outer pad, which is supported by the outer body portion 3, against the outer-side surface of the rotor 6, with the outer pistons being respectively fitted into the outer cylinders in an oil tight manner. Accordingly, the rotor 6 is durably interposed between the inner pad 10 and the outer pad on both sides in the axial direction. As a result, braking is performed due to friction between the inner pad 10 and the outer pad and both the axial side surfaces of the rotor 6. When the brake is applied, torque applied to each of both the inner pad 10 and the outer pad is borne by an entry-side torque receiving portion 15 and an exit-side torque receiving portion 16 which are respectively provided on an inner side and an outer side with the rotor 6 interposed therebetween. In the illustrated structure, the entry-side torque receiving portion 15 and the exit-side torque receiving portion 16 are respectively formed of the projecting wall portions 11, 11 and the metal support fittings 12, 12.
The opposed-piston disc brake caliper requires performances illustrated in (1) and (2).
(1) Improvement in Cooling Capacity (Heat Dissipation Capacity)
When the brake is applied, heat is produced due to friction between the side surfaces of the rotor and linings of both the inner pad and the outer pad, and the insufficient cooling of the rotor and both the inner pad and the outer pad may reduce a frictional coefficient, and decrease braking force. Heat is transmitted from the inner pad and the outer pad to the caliper via the torque receiving portions, and a high temperature of the caliper may increase the temperature of a brake fluid present inside of the caliper, and decrease braking force as well.
(2) Ensuring Rigidity
When the brake is applied, as a reaction to the event in which both the inner pad and the outer pad are pressed against both the side surfaces of the rotor by the inner pistons and the outer pistons, force is applied to both the inner body portion and the outer body portion in a direction in which the inner body portion and the outer body portion move away from each other. For this reason, when the rigidity of the caliper is not sufficient, both the inner body portion and the outer body portion may be elastically deformed in the direction in which the inner body portion and the outer body portion move away from each other, and a so-called braking force may not be obtainable. In a case where the rigidity is not sufficient, when the brake is applied, elastic deformation may occur such that the outer body portion is displaced relative to the inner body portion in a rotational direction of the rotor, and vibration or noise may occur.
The opposed-piston disc brake caliper requires the performances illustrated in (1) and (2); however, the obtaining of the performances illustrated in (1) and (2) is difficult.
For example, in the caliper 1 with the structure in the related art illustrated in FIGS. 15 to 17, inner end edges of the entry-side connection portion 4 and the exit-side connection portion 5 extend further inwards (to the center) than the entry-side torque receiving portion 15 and the exit-side torque receiving portion 16 in the circumferential direction, with circumferential end edges of the opening portion 7 being partitioned off by the inner end edges. For this reason, this is disadvantageous in that both the entry-side torque receiving portion 15 and the exit-side torque receiving portion 16 are not efficiently cooled. In order to improve cooling capacity, the area of the opening portion 7 is deemed to be increased by moving the positions of the inner end edges of the entry-side connection portion 4 and the exit-side connection portion 5 further outwards than the illustrated positions in the circumferential direction. When such a configuration is adopted, it is possible to improve the cooling capacity of the rotor 6 and both the inner pad 10 and the outer pad, and it is possible to easily cool both the entry-side torque receiving portion 15 and the exit-side torque receiving portion 16. However, when such a configuration is adopted, the circumferential width dimensions of both the entry-side connection portion 4 and the exit-side connection portion 5 are decreased, and thus, it is not easy to ensure the rigidity of the caliper 1. As such, it is not easy to improve the cooling capacity and to ensure the rigidity of the opposed-piston disc brake caliper.
[Patent Document 1] JP-A-2010-078055